Oak, Garry (Quercus)-Pit scale

Asterodiaspis species


Pest description and crop damage Adult scale are covered with a hard shell and are about 0.06 inch in diameter. They may be brown, gold, or greenish. They feed on twigs and small branches, with young wood most commonly infested. Pit scale feeding causes the tissue of the twig to swell around the insect. The growth makes the scale appear to be in a pit on the bark. Numerous scale on a twig cause it to appear roughened. Severe infestations cause twig dieback. Heavy infestations of pit scale combined with drought stress or anthracnose (a fungal disease) can result in severe weakening or death of trees.

Biology and life history Scale overwinter as mature females in pits on the twigs. Crawlers are produced in the late spring. These do not move far and typically colonize current season and 1-year-old wood. After settling to suck plant juices, the crawlers do not move for the remainder of their life cycle. There is one generation per year.

Management-chemical control


Apply to control the immature crawler stage, usually in late spring to early summer. Scout for crawlers and gather life history data. Adding 1% horticultural oil increases effectiveness. Trees sometimes are injured when sprayed while under stress due to drought, root pruning, etc.

For more information

Johnson, W.T. and H.H. Lyon (1991), Insects That Feed on Trees and Shrubs, 2nd ed., Cornell University Press (p. 352).